fixed native Lapack detection script on Mac/iOS (where native Lapack is a part of Accelerate framework)

cmake/OpenCVFindLAPACK.cmake

@@ -31,11 +31,18 @@ macro(ocv_lapack_check)
   else()
     # adding proxy opencv_lapack.h header
     set(CBLAS_H_PROXY_PATH ${CMAKE_BINARY_DIR}/opencv_lapack.h)
-    set(_lapack_include_str "extern \"C\" {\n\#include \"${OPENCV_CBLAS_H_PATH_${_lapack_impl}}\"")
+    if(APPLE)
+        set(_lapack_include_str_extern_C "")
+        set(_lapack_include_str_extern_C_end "")
+    else()
+        set(_lapack_include_str_extern_C "extern \"C\" {\n")
+        set(_lapack_include_str_extern_C_end "}\n")
+    endif()
+    set(_lapack_include_str "${_lapack_include_str_extern_C}\#include \"${OPENCV_CBLAS_H_PATH_${_lapack_impl}}\"")
     if(NOT "${OPENCV_CBLAS_H_PATH_${_lapack_impl}}" STREQUAL "${OPENCV_LAPACKE_H_PATH_${_lapack_impl}}")
       set(_lapack_include_str "${_lapack_include_str}\n#include \"${OPENCV_LAPACKE_H_PATH_${_lapack_impl}}\"")
     endif()
-    set(_lapack_include_str "${_lapack_include_str}\n}\n")
+    set(_lapack_include_str "${_lapack_include_str}\n${_lapack_include_str_extern_C_end}")
     # update file contents (if required)
     set(__content_str "")
     if(EXISTS "${CBLAS_H_PROXY_PATH}")